An accumulation of genetic changes underlies the development and progression of cancer, resulting in cells that differ from normal cells in their behavior, biochemistry, genetics, and microscopic appearance. Mutations in DNA that cause changes in the expression level of key proteins, or in the biological activity of proteins, are thought to be at the heart of cancer. For example, cancer can be triggered in part when genes that play a critical role in the regulation of cell division undergo mutations that lead to their over-expression.
Oncogenes are involved in the dysregulation of growth that occurs in cancers. An example of oncogene activity involves protein kinases, enzymes that help regulate many cellular activities, particularly signaling from the cell membrane to the nucleus, thus initiating the cell""s entrance into the cell cycle and controlling several other functions.
Oncogenes may be tumor susceptibility genes, which are typically up-regulated in tumor cells, or may be tumor suppressor genes, which are down-regulated or absent in tumor cells. Malignancies can arise when a tumor suppressor is lost and/or an oncogene is inappropriately activated. When such mutations occur in somatic cells, they result in the growth of sporadic tumors.
Hundreds of genes have been implicated in cancer, but in most cases relationships between these genes and their effects are poorly understood. Using massively parallel gene expression analysis, scientists can now begin to connect these genes into related pathways.
Phosphorylation is important in signal transduction mediated by receptors for extracellular biological signals such as growth factors or hormones. For example, many cancer causing genes (oncogenes) are protein kinases, enzymes that catalyze protein phosphorylation reactions, or are specifically regulated by phosphorylation. In addition, a kinase can have its activity regulated by one or more distinct protein kinases, resulting in specific signaling cascades.
Many of the intracellular physiological activities in mammalian cells that involve Ca++ as a second messenger are mediated by calmodulin (CAM). This ubiquitous Ca++-binding protein has an ability to activate a variety of enzymes in a Ca++-dependent manner. Among these enzymes are Ca++ and calmodulin-dependent cyclic-nucleotide phosphodiesterase (CaM-PDE) and the calmodulin-dependent kinases.
CaM-kinases are involved in regulation of smooth muscle contraction (MLC kinase), glycogen breakdown (phosphorylase kinase), and neurotransmission (CaM-kinase I and CaM-kinase II). CaM-kinase I phosphorylates a variety of substrates including the neurotransmitter related proteins synapsin I and II, the gene transcription regulator, CREB, and the cystic fibrosis conductance regulator protein, CFTR (Haribabu et al. (1995) EMBO Journal 14:3679-86). CaM-kinase II also phosphorylates synapsin at different sites, and controls the synthesis of catecholamines in the brain through phosphorylation and activation of tyrosine hydroxylase.
Many of the CaM-kinases are activated by phosphorylation in addition to binding to CaM. The kinase may autophosphorylate, or be phosphorylated by another kinase as part of a xe2x80x9ckinase cascadexe2x80x9d. A variety of substances inhibit the activation properties of calmodulin on the calmodulin-dependent enzymes. It has been shown that drugs that inhibit calmodulin sensitive processes are also potent inhibitors of the growth and viability of tumor cells (Hait et al. (1985) Biochem Pharmacol. 34:3973-3978; Hait et al. (1986) J. Clin. Oncol. 4:994-1012). Thus, substances that inhibit calmodulin-mediated enzyme activites may affect cell viability, and possibly other cellular phenomena, through their interactions with calmodulin.
Members of the CaM-kinase cascade in the cytosol regulate cell survival through activation of protein kinase B, and transcription through indirect activation of MAP kinases. Activated MAP kinases translocate to the nucleus, where they phosphorylate transcription factors. CaM-kinase IV can also phosphorylate and inactivate type I adenylate cyclase, thereby decreasing cyclic AMP levels.
Each member of the CaM-kinase cascade has a catalytic domain adjacent to a regulatory region that contains an overlapping auto-inhibitory domain (AID) and the CaM-binding domain (CBD). An interaction between the AID and the catalytic domain maintains the kinase in an inactive conformation by preventing binding of protein substrate as well as Mg++-ATP. Binding of Ca++-CaM to the CBD alters the conformation of the overlapping AID such that it no longer interferes with substrate binding; the kinase is therefore active. As in the cases of other protein kinases, CaMKI has a catalytic cleft between its upper and lower lobes, which are responsible for binding Mg++-ATP and protein substrates, respectively. At the base of their catalytic clefts, many protein kinases, including CaMKI and CaMKIV, have an activation loop containing a threonine residue whose phosphorylation strongly augments kinase activity.
Cloning procedures aided by homology searches of EST databases have accelerated the pace of discovery of new genes, but EST database searching remains an involved and onerous task. More than 1.6 million human EST sequences have been deposited in public databases, making it difficult to identify ESTs that represent new genes. Compounding the problems of scale are difficulties in detection associated with a high sequencing error rate and low sequence similarity between distant homologues.
Relevant Literature
The use of genomic sequence in data mining for signaling proteins is discussed in Schultz et al. (2000) Nature Genetics 25:201.
The CaM-kinase protein family has been reviewed, for example by Heist et al. (1998) Cell Calcium 23(2-3):103-14; and Soderling (1999) Trends Biochem Sci 24(6):232-6. Inhibitors of calmodulin mediated enzymes are described in U.S. Pat. No. 5,386,019. The effects of CaM-kinase inhibitors include inhibition of DNA synthesis and slowed progression through S phase, discussed by Minami et al. (1994) Biochem Biophys Res. Comm. 199:241-248; and Williams et al. (1996) Biochem Pharmacol. 51:707-715.
The gene accession number for EST clone K283 is AA838372.
This invention relates to novel CaMK-X1 nucleic acid compositions and their encoded polypeptides and variants thereof, to genes corresponding to these nucleic acids and to proteins expressed by the genes. The invention also provides diagnostics and therapeutics comprising such novel human nucleic acids, their corresponding genes or gene products, including probes, antisense nucleotides, and antibodies. The nucleic acids of the invention encode a protein designated as CaMK-X1. CaMK-X1 is associated with cellular transformation and regulation. The upregulated expression of this gene in cancer tissues provides a genetic target to screen therapeutics for the treatment of cancer and various other diseases. In addition, the sequence is used to form antisense compositions for the control of disease, to perform research using transgenic or knockout animal models, and research reagents such as antibodies, cell assays, and chromatographic reagents.
The nucleic acid compositions find use in identifying homologous or related genes; for production of the encoded protein; in producing compositions that modulate the expression or function of its encoded protein; for gene therapy; in mapping functional regions of the protein; and in studying associated physiological pathways. In addition, modulation of the gene activity in vivo is used for prophylactic and therapeutic purposes, such as treatment of cancer, identification of cell type based on expression, and the like.